From: "rosenfeld (Rodrigo Rosenfeld Rosas)" <rr.rosas@...>
Date: 2012-06-25T21:24:37+09:00
Subject: [ruby-core:45832] [ruby-trunk - Feature #6641] Hash.auto constructor


Issue #6641 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).


Maybe something like Hash.with_default{[]}. "with_default" could be both a class and an instance method so that you could have something like {a: 1, b: 2}.with_default(0).merge... It would always return the hash itself...

Groovy has a I guess that's how default values work in Groovy (not quite the same behavior). In Groovy you can define default values as [:].withDefault{0}. You can optionally use the block argument as the key.

So I guess it would be great if Ruby with_default supported all those syntax below:

Hash.with_default(0)
Hash.with_default{Time.now}
Hash.with_default{|k| k.to_sym}
{}.with_default(0)
{}.with_default{Time.now}
{}.with_default{|k| k.to_sym}
----------------------------------------
Feature #6641: Hash.auto constructor
https://bugs.ruby-lang.org/issues/6641#change-27408

Author: trans (Thomas Sawyer)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


=begin
It is not uncommon to need a Hash following the pattern:

  Hash.new{ |h,k| h[k]={} }

Another common example:

  Hash.new{ |h,k| h[k]=[] }
  
This is common enough that it would very nice if we could have a more concise form, e.g.

  Hash.auto{ {} }

Or for the second example:

  Hash.auto{ [] }

Pure Ruby implementation is pretty simple:

  def Hash.auto
    Hash.new{ |h,k| h[k] = yield }
  end

I think it would be nice to have in Core.

This is secondary, but it just occurred to me. Could there even be a literal notation for the above? Something like:

  {}([])

?
=end



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